Method and device for controlling the speed of an internal combustion engine during a deceleration phase

ABSTRACT

The process assures the correction of the control of an actuator acting on the speed as a function of the error E=N c  -N between a set-point speed (N c ) and the actual speed (N), and of the time derivative (E&#39;) of this error. A correction (Δu) for the control of the actuator is derived from the addition of first (Δu 1 ) and second (Δu 2 ) partial corrections which are functions of the speed error (E) and the time derivative (E&#39;) of this error, respectively. These corrections are defined as a function of the relative position of the value of the error, or of the error derivative, with respect to at least two predetermined values of the error (or the derivative of the error), each of which has an associated predetermined value of the partial correction Δu 1  (or Δu 2 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process and a device for controllingthe speed of an internal combustion engine during a deceleration phase,and more specifically to a process and a device of this type whichoperate by correcting the control of an actuator which acts on thisspeed as a function of the deviation between a set-point speed and theactual speed.

Internal combustion engines, particularly those which propelautomobiles, run at variable speeds, the control and/or adjustment ofwhich is often delicate, particularly during the deceleration phase. Adeceleration phase usually begins when the driver lifts his foot off theaccelerator. The object of speed control during such a phase is toassure the return of this speed to a set-point speed, the adjustment ofthe speed around this set-point speed despite potential disturbances,and the passage through various transitory phases such as a "driven"deceleration phase in which the vehicle runs with an engaged gear boxratio, or an engine start-up phase.

In all of these circumstances, control of the speed is quite delicate,since it is known that the stability of an engine at low speed isdifficult to assure and that the reactions of the engine are difficultto model. Moreover, the conditions for the onset of a deceleration phasecan vary considerably, for example in relation to the driver's action onthe accelerator pedal, the engine coolant temperature, the airtemperature, and the potential presence of random disturbances due tothe engagement of an electrical (lighting device, ventilator) ormechanical (air conditioner, power steering) device. The speed controlmust also take into account other constraints associated with thedriver's comfort (noise level, vibrations, jerking) and to standardsrelated to the pollution of the environment by the exhaust gases fromthe engine.

2. Description of the Related Art

At present, in order to assure control of the speed of the engine duringa deceleration phase, closed loop control devices with "supervised"PID-type controllers are commonly used. A device of this type isdescribed in German patent Disclosure DE-A-4 215 959, for example, whichrelies on fuzzy logic to adjust the P, I and D terms of the controller.The result is time-consuming, tedious tuning of the controller in orderto adapt it to each type of engine. The PID adjustment is alsodisadvantageous in that it takes into account only certain aspects ofthe operation of the engine, and that it is not entirely satisfactoryfrom the standpoint of "robustness", since engine aging or manufacturingtolerances for engines can unfavorably affect the operation of a"supervised" PID controller.

A process for controlling the deceleration speed of an internalcombustion engine, which is based entirely on experimental resultsimplemented with the aid of fuzzy logic and is therefore likely, apriori, to have greater robustness and flexibility, is known from SAEdocument No. 900594, published by the Society of Automotive Engineers ofthe United States of America. However, the process described requiresthe utilization of tables and complex operators which take up a lot ofspace in the memory of the computer used to implement the process, whichmoreover involves long calculation times.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a process forcontrolling the speed of an internal combustion engine during adeceleration phase which results in significant reductions both in thememory space necessary in the computer used for this purpose and in thecalculation times.

Another object of the present invention is to provide a process of thistype which will be satisfactory from four points of view: robustness,resistance to disturbances, ease of adjustment and the pleasure ofdriving a vehicle propelled by such an engine, in all phases ofdeceleration.

Yet another object of the present invention is to produce a device forimplementing this process.

These objects of the invention, as well as others which will becomeapparent through a reading of the description which follows, areachieved by means of a process for controlling the speed N of aninternal combustion engine in a deceleration phase by correcting thecontrol of an actuator which acts on this speed as a function of theerror E=Nc-N between a set-point speed Nc and the actual speed N, andthe time derivative E' of this error, which process is remarkable inthat it derives a correction u for the control of the actuator from alinear combination of first (Δu₁) and second (Δu₂) partial correctionswhich are functions of the speed error E and the time derivative E' ofthis error, respectively, which corrections are defined as a function ofthe relative position of the value of the error, or of the derivative ofthe error, with respect to at least two predetermined values of theerror (or the derivative of the error), each of which has an associatedpredetermined value of the partial correction Δu₁ (or Δu₂).

As will be seen below, the division of the correction into two partialcorrections, each of which is a function of only one of the parametersE, E', makes it possible to reduce the quantity of information necessaryto the execution of the process, and therefore the memory spacerequired, as well as the calculation time for the correction.

In a first mode of implementation of the process according to theinvention, the error E and the derivative E' of this error are fuzzifiedand processed by separate sets of fuzzy logic rules, so that afterdefuzzification, they provide the first (Δu₁) and second (Δu₂) partialcorrections. In a second mode of implementation of the process accordingto the invention, the functions which link the first (Δu₁) and second(Δu₂) partial corrections to the speed error E and the derivative E' ofthis error, respectively, are defined by characteristic points, andintermediate values for the corrections are obtained by interpolationbetween these characteristic points.

In order to implement the process according to the invention, a deviceis used which comprises a) means for issuing a first signal representingthe speed error E and a second signal representing the derivative E' ofthis error, derived from a signal issued by a sensor of the actual speedN of the engine and from a signal representing a predetermined value ofthe set-point deceleration speed Nc and b) first and second controllerssupplied with the first and second signals, respectively, for deliveringthe first and second partial corrections, and c) means supplied withthese partial corrections and with input from the source of a nominalcontrol signal from the actuator for delivering a final control signalfor the actuator.

Other characteristics and advantages of the present invention willbecome apparent through a reading of the description which follows andthrough an examination of the appended drawing, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a function diagram of the control device according to thepresent invention;

FIGS. 2 and 3 are diagrams which illustrate a first mode ofimplementation of the process according to the invention, which relieson a control in fuzzy logic;

FIGS. 4 and 5 are graphs which illustrate a second mode ofimplementation of the process according to the invention, which relieson control functions defined by characteristic points;

FIG. 6 is constituted by two graphs which illustrate the operation ofthe process according to the invention in a phase of compensation for amisfire; and

FIG. 7 is constituted by two graphs which illustrate the operation ofthe process according to the invention during a phase of compensationfor a disturbance such as the engagement, during a deceleration phase,of an electrical or mechanical device installed in a vehicle propelledby the internal combustion engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is intended to control an internal combustionengine propelling an automobile during a deceleration phase, the enginebeing located in a conventional environment of sensors, actuators andelectronic means for controlling these actuators. These means usuallycomprise an electronic computer with input from a variable reluctancesensor, for example, coupled with a gear wheel mounted on the outputshaft of the engine, for sending the computer a signal representing theengine rpm (or speed), which computer also receives input from apressure sensor mounted inside the intake manifold of the engine forproviding a signal which represents the pressure of the air admittedinto the engine. Other signals originating from engine coolanttemperature sensors, air temperature sensors, etc., or from an oxygenprobe placed in the exhaust gases of the engine, can also be sent to thecomputer in the conventional way.

This computer is equipped with the hardware and software necessary tothe development and emission of signals for controlling actuators suchas a fuel injector, a spark plug ignition circuit or an additional aircontrol valve which short-circuits a throttle valve for controlling thequantity of air which enters the engine through the intake manifold.

It has been decided that as an illustrative and non-limiting example,the control process according to the invention will be described belowin terms of a control of the engine by means of an action on the openingtime of a fuel injector. However, it will be immediately apparent to oneskilled in the art that the same control process could be modeledthrough an action on the opening of an additional air control valve, onthe timing of the opening of a plurality of fuel injectors, on the angleof the opening of the electrically driven throttle valve, or through acombination of actions on these various actuators.

In FIG. 1 of the appended drawing, it is apparent that the deviceaccording to the invention comprises means 1 supplied with signals whichrepresent the actual speed N of the engine and the set-pointdeceleration speed Nc (Nc=600 rpm, for example) for forming an errorsignal E=Nc-N. It must be noted that the set-point deceleration speedwould not necessarily have to be fixed, but on the contrary, could be afunction of various parameters such as the engine coolant temperature,or the possible presence of a disturbance such as the engagement of amechanical or electrical device.

The device in FIG. 1 also comprises means 2 for forming a signal whichrepresents the time derivative E' of the error E and control means or"controllers" 3 and 4 which are supplied with the signals E and E',respectively, possibly filtered by a first-order recursive filter inorder to avoid any "noise" phenomena. The controllers 3 and 4 generatepartial correction signals Δu₁ and Δu₂, respectively. Advantageously,but only in an optional way, the device may also comprise amplifiers 12,13 with gains G₁, G₂, respectively, supplied with the signals Δu₁, Δu₂,respectively. The signals G₁.Δu₁ and G₂.Δu₂ thus obtained as output fromthe amplifiers are added at 5 in order to constitute a global correctionΔu of a nominal control signal for an actuator (not shown), for examplea fuel injector in the engine, as seen above.

A supervisor 14 adjusts the gains G₁, G₂ of the amplifiers 12, 13 insuch a way as to vary the relative weight of the corrections Δu₁ and Δu₂in the linear combination Δu as a function of, for example, the enginespeed at the onset of a deceleration speed phase, and possibly of theload carried by the engine.

The signal Δu can be processed in a saturator 6 in order to limit thedynamics of the control, which is conventional. Likewise, the outputfrom the saturator can be parallel processed in an amplifier 7 with again G₁ and in an integrator 8 so as to form a "direct" correction G₃.Δuand an "integral" correction G₄ ∫Δu.dT which are added at 9, then at 10,to a nominal control 11 of the actuator in order to finally constitutethe control signal U for this actuator.

Conventionally, the integral correction 8 is provided in order tocorrect the nominal control when it is no longer suitable due to theapplication of a continuous or slow variation load to the engine, as isthe case when a power steering device is engaged, for example.

Since the processing executed in the blocks 6, 7, and 8 of the diagramin FIG. 1 is optional, from this point forward "u" will mean thecorrection signal for the nominal control of the actuator, whether ornot it has been subjected to this processing.

As will immediately be apparent to one skilled in the art, the controldevice described above can easily be incorporated into the computermentioned above, simply by installing the necessary hardware andsoftware into this computer. It will be noted that in the deviceaccording to the invention, up to this point the error E and itsderivative E' have been taken into account separately in two distinctcontrollers 3 and 4. The reasons why this disposition is advantageouswith regard to reducing the memory requirements of the computer and thecalculation time will now be explained in connection with FIGS. 2 and 3.

In a first embodiment of the device according to the inventiondiagrammed in FIG. 3, the controllers 3 and 4 are designed to work infuzzy logic. For this purpose, the variables E and E' are "fuzzified"using the conventional processes for defining membership classes, forexample NG through PG, and functions for membership in these classeswhich can have triangular shapes as represented in FIG. 2, or othershapes which are well known to one skilled in the art.

The membership classes NG through PG which appear in this figurecorrespond to the following linguistic labels:

PG: positive large

PM: positive medium

PP: positive small

ZE: zero

NP: negative small

NM: negative medium

NG: negative large

It will be noted in FIG. 2 that the membership functions NP and PP ofthe variable E', represented by dotted lines, do not meet at the pointE'=0. This particular disposition makes it possible to create, in theinterval from E'-to E'+, an artificial hysteresis of the partialcorrection which is a function of the derivative, in order to avoid thedisturbances linked to noise at the measurement of E' near its nullvalue. In fact, in this interval, only the membership function ZE (zero)is activated.

Each controller is loaded with seven rules drawn from the experience ofone skilled in the art, which translate observations such as:

"The greater the input (E or E'), the greater the correction must be",which produces rules like:

"If the input (E or E') belongs to the class NG, then the correctionbelongs to the class NG" or

"If the input (E or E') belongs to the class PG, the correction belongsto the class PG".

The fuzzy corrections determined in this way are then defuzzified in theconventional way in order to furnish the partial corrections Δu₁ and Δu₂which are added in order to form the global correction Δu for thenominal control U.

In this first embodiment in fuzzy logic, the "fuzzification" step forthe value of the error (or the derivative of the error) makes itpossible to determine a "relative position" of this value with respectto the values which correspond to the maxima of the membership functionsrepresenting the classes from which it is derived, a position expressedby the degrees of membership in these classes plotted on the graphs inFIG. 2. The "defuzzification" step determines, as a function of thesedegrees of membership, the relative position of the control with respectto the control values associated with the control classes, whichcorrespond through the set of rules, to the classes of the error (or thederivative of the error) in question. By thus defining each of thecorrections Δu₁, Δu₂ relative to two predetermined values according tothe invention, the drawbacks of the conventional or "supervised" PIDcorrections, applied in "segments" of values of E or E' which arederived from the nondefinition of the connections of these segments, areadvantageously avoided.

An important advantage of the control process according to the inventionpresently appears in reference to the control process described in theabove-mentioned SAE document No. 900594, which also relies on fuzzylogic. In this document, however, the fuzzy controller used executes aset of rules diagrammed in a table with two entries E and E'. Fuzzifyingthese inputs into seven membership classes results in a table of 7×7=49rules. By comparison, the present invention makes use of two controllerseach of which executes 7 rules, for a total of 14 rules. It is clearthat the memory space required of the computer by these 14 rules is farless than that for the 49 rules in the table according to the teachingsof the prior art. The calculation time for the correction of the controlis also reduced in proportion to the reduction of the number of rulestaken into account during the calculation.

The graphs in FIGS. 4 and 5 illustrate the operating principle of asecond embodiment of the device according to the invention, which alsotakes advantage of the presence in this device of two specializedcontrollers which are sensitive to the error E and to the derivative E'of this error, respectively. Rather than using fuzzy logic as describedpreviously, the processing of the data known to one skilled in the artfrom experience is further simplified by formalizing the data in twofunctions Δu₁ =f(E) and Δu₂ =f'(E') as shown in FIGS. 4 and 5,respectively. Advantageously, each function is defined by particularpoints, with linguistic labels NG through PG chosen in reference tothose used above in fuzzy logic; the analogy, however, ends there. Fromthese particular points, the controllers derive the outputs Δu₁ and Δu₂from simple interpolations between the particular points which frame aparticular entry value E, E', which simplifies and further reduces thecalculations as compared to the fuzzy logic calculations suggested inconnection with the embodiment in FIGS. 2 and 3.

Incidentally, it will be noted that the values associated with each ofthe linguistic labels can be different for each of the entry variablesE, E'. In particular, the asymmetry of the slopes of the graphs around 0(ZE) for the variable E', will be noted.

The advantages of the present invention will now be illustrated througha description of two typical examples of the operation of the controldevice, one relating to the reaction of this device to the appearance ofa misfire (see the graphs in FIG. 6), the other relating to the reactionof this device to the appearance of a disturbance such as the engagementof an electrical or mechanical device installed in an automobilepropelled by the engine (see the graphs in FIG. 7). In both cases, thecontrol process by means of interpolation illustrated in FIGS. 4 and 5is used and is applied, merely by way of example, to an internalcombustion engine of the "two stroke" type supplied with a suitably leanair/fuel mixture during the deceleration adjustment phase.

The result is unstable operation at low speed, essentially due toincomplete or absent combustion of the air/fuel mixture present in thecylinders of the engine. It is said in this case that misfires areobserved. In a misfire, a random phenomenon, a drop in the speed N,which may cause the engine to stall, is observed. At the moment of thisdrop in speed (time t₁ in the graphs N(t) and Δu(t) in FIG. 6), thedevice according to the invention strongly increases the injection timein order to allow the restoration of the speed N. In reading the graphsΔu(t) in Δu₂ FIGS. 6 and 7, it will be noted that Δu is a standardizedcorrection, varying between -1 and +1. From the moment the restorationof the speed has occurred (time t₂, FIG. 6), it is necessary to avoidexcessively reducing the injection time, so as not to risk encouraginganother misfire. Then, a slight overshooting of the set-point speed dueto fuel-rich combustion is observed (time t₃, FIG. 6), but in this casethere is no need to correct the injection time appreciably. This type ofcombustion is due to the surplus of fuel injected at the precedingtimes.

In order to obtain this performance, the characteristic points of thefunction represented in FIG. 5 are asymmetrical around the point 0 (ZE)so as to generate a control Δu₂, which is also asymmetrical. At time t₂(FIG. 6), the derivative of the error is seen as positive medium (PM),thus generating a positive medium (PM) correction Δu₂. On the otherhand, at time t₂, although the derivative of the error has the sameamplitude in absolute value as at time t₁, it will be seen as beingnegative small (NP), thus generating a negative small (NP) correctionΔu₂. During the entire misfire, the error remains very small in absolutevalue, as does the correction Δu₁ (see FIG. 4), with the essentials ofthe correction Δu of the control of the injection time in this casecoming from the controller 4 with the output Δu₂ (see FIG. 5).

Refer now to FIG. 7 of the appended drawing in which the graphs N(t) andΔu(t) illustrate the correction according to the invention of a drop inthe speed N due to the occurrence, during a deceleration phase, of theengagement of a mechanical (a power steering device, for example) orelectrical (air conditioner, etc.) device.

The disturbance occurs at time t₁. Roughly the same initial conditionsfor the speed error and the derivative of this error exist as were foundduring the appearance of a misfire. The reaction of the device accordingto the invention therefore consists of strongly increasing the injectiontime in such a way that a rapid reaction prevents the engine fromstalling.

At time t₂, the progressive restoration of the engine speed begins, butin this case a strong correction Δu of the injection time is maintainedso that this restoration can proceed. At time t₃, the speed haspractically regained the set-point value N_(c) and the device thenreduces the correction of the injection time in order to avoidovershooting this set-point value.

It will be observed that, compared to the compensation for a misfire(see FIG. 6), the compensation for the disturbance is slower. Thecorrection u of the injection time therefore chiefly involves the speederror E (see graph in FIG. 4), and therefore the controller 3, while thederivative E' remains very low during the increase in speed.

The characteristic points of the graph in FIG. 4 are adjusted so as toassure the correction of the injection time in this situation. Thus, atthe occurrence of the disturbance, the error E is situated around thepoint PM, and the controller responds to this input with a partialcorrection Δu₁ at the level PM. The characteristic point PP of the errorE is adjusted as a function of the speed error at time t₃ so that thepartial correction Δu₁ is at the level PP when the speed N approachesthe set-point speed N_(c).

The present invention contributes numerous advantages. In addition tothe above-mentioned reductions in required memory space and calculationtime, the control strategies developed by the process according to theinvention also prove to be quite satisfactory with regard to robustness,resistance to disturbances, ease of adjustment and driving comfort.

These advantages are specifically derived from the capability providedby the process according to the invention for breaking down theoperation of the engine, at the deceleration speed, into four verydistinct situations:

1) onset of deceleration adjustment, uncoupled engine (large E, E'),

2) engine driven by the vehicle (large E, small E')

3) stabilized deceleration (small E, E')

4) occurrence of a misfire or a disturbance (small E, large E'), each ofthese situations being able to be processed by means of differentadjustments of the characteristic points on the graphs in FIGS. 4 and 5or and 5 or by "fuzzy" control rules arranged in the tables in FIG. 3.

It is understood that the invention is not limited to the embodimentdescribed and illustrated, which is given only by way of example.Specifically, it encompasses the control of any internal combustionengine, not just that of a two stroke engine supplied with a "lean"mixture.

We claim:
 1. A method of controlling the speed of an internal combustionengine during a deceleration phase,wherein the speed of the engine isaffected with a controlled actuator connected thereto, the method whichcomprises: defining a speed error E=N_(c) -N, where N_(c) is a set-pointspeed, and N is an actual speed of the engine, and calculating a timederivative E' of the speed error E; deriving a correction for a controlof the actuator from a linear combination of a first partial correctionand a second partial correction, wherein the first partial correction isa function of the speed error E and the second partial correction is afunction of the time derivative E' of the speed error, and said partialcorrections being defined as a function of a relative position of avalue of the speed error E and of the time derivative E' thereof,respectively, relative to at least two predetermined values of the speederror E and of the time derivative E' thereof, each of which has anassociated predetermined value of the partial corrections; fuzzifyingthe speed error E and the time derivative E' thereof, processing thespeed error E and the time derivative E' with separate sets of fuzzylogic rules, subsequently defuzzifying and producing the first andsecond partial correction; filtering disturbances linked to noise at themeasurement of the derivative near its null value, by fuzzifying thetime derivative of the speed error in the fuzzifying step with a set ofmembership classes which do not overlap within a predetermined intervalof values of E' around E'=0; and correcting a control of the actuatorand thereby affecting the speed of the engine as a function of the speederror E and of the time derivative E' thereof.
 2. The method accordingto claim 1, which comprises defining the functions linking the first andsecond partial corrections to the speed error and to the timederivative, respectively, with characteristic points, and obtainingintermediate values of the partial corrections by interpolation betweenthe characteristic points.
 3. The method according to claim 1, whichcomprises saturating the correction for the control of the actuator forlimiting the dynamics of the correction.
 4. The method according toclaim 3, which further comprises processing the saturated correctionobtained in the saturating step with means for forming a directcorrection and an integral correction, and adding a sum of the directand integral corrections to a nominal control of the actuator fordefining a control signal for the actuator.
 5. The method according toclaim 1, wherein the correction of the control of the actuator has theform:

    Δu=G.sub.1.Δu.sub.1 +G.sub.2.Δu.sub.2

where G₁ and G₂ are coefficients which are adjustable as a function ofoperating parameters of the engine.
 6. A device for controlling thespeed of an internal combustion engine during a deceleration phase,wherein the speed of the engine is affected with a controlled actuatorconnected thereto, comprising:a) a device receiving a sensor signalrepresenting an actual speed N of the engine and a signal representing apredetermined set-point speed N_(c), said device defining a speed errorE=N_(c) -N as a first signal, and calculating a time derivative E' ofthe speed error E as a second signal; b) a first fuzzy logic controllerreceiving the first signal and forming a first partial correction, asecond fuzzy logic controller receiving the second signal and forming asecond partial correction; a device for forming a linear combination ofthe first partial correction and the second partial correction andderiving a correction for a control of the actuator from the linearcombination; means for filtering disturbances linked to noise at themeasurement of the derivative near its null value, by fuzzifying thetime derivative of the speed error with a set of membership classeswhich do not overlap within a predetermined interval of values of E'around E'=0; and c) means receiving the correction derived in the linearcombination and a signal from a source of a nominal control signal forthe actuator, and issuing a corrected final control signal for theactuator and thereby setting the speed of the engine as a function ofthe speed error E and of the time derivative E' thereof.
 7. The deviceaccording to claim 6, wherein said first and second controllers includea memory for storing the functions which link the speed error and thetime derivative thereof to the first and second partial corrections,respectively.
 8. The device according to claim 7, wherein the memorystore characteristic points of the functions, and said controllerscomprise means for interpolating between the characteristic points. 9.The device according to claim 6, wherein said means issuing the finalcontrol signal for the actuator form a signal

    Δu=G.sub.1.Δu.sub.1 +G.sub.2.Δu.sub.2

where G₁ and G₂ are coefficients, and including a, supervisor foradjusting the coefficients G₁ and G₂ as a function of operatingparameters of the engine.
 10. The device according to claim 6, whereinsaid means include a saturator for saturating the linear combination.11. The device according to claim 10, wherein said means furthercomprise a correction device receiving an output from said saturator,said correction device generating a direct correction and an integralcorrection added to the nominal control signal for the actuator fordefining the final control signal for the actuator.
 12. The deviceaccording to claims 6, wherein the actuator controls a parameterselected from the group consisting of an opening of an additional aircontrol valve, an opening time for a fuel injector, a timing of anopening of a plurality of fuel injectors, and an opening angle of anelectrically driven throttle valve.